1. Field of the Invention
This invention relates generally to a system for supplying into and, more particularly, to a system for supplying colored inks to an on-demand-type ink jet printer.
2. Description of Background
A conventional so-called on-demand-type ink jet printer records data on a recording medium, such as a sheet of paper or film, by discharging ink droplets from a nozzle in accordance with a printing signal. This kind of printer has recently rapidly spread in popularity, because the size and the cost of the printer have been steadily minimized.
On the other hand, in recent years, the procedure referred to as desk-top publishing using a personal computer has become increasingly popular, particularly in offices. Moreover, requests for outputting not only characters and graphics but also colored natural images, such as photos, have also been recently increasing. Thus, a lot of ink is required to print not only characters and graphics but also natural images.
This kind of on-demand-type ink jet printer typically includes an ink tank mounted on a carriage for holding a print head and feeding ink to the print head simultaneously with the printing operation of the print head. This kind of ink supply is hereinafter referred to as the carriage-mounting type. Another approach to supplying ink is to use an ink tank arranged separately from the print head and to feed ink to the print head through a tube. This kind of ink supply hereinafter referred to as the tube type.
FIG. 21 shows a carriage-mounting-type serial ink jet printer, in which the ink jet printer 1 is constructed so that a platen 6 is rotated in accordance with a rotary drive supplied to the platen 6 through a motor 2, pulley 3, belt 4, and platen shaft 5. A feed screw 7 is mounted nearby to the platen 6 in parallel with the longitudinal axis of the platen 6 and a carriage 10 on which a cartridge-type ink tank 8 and a print head 9 are integrally mounted is threadedly engaged with the feed screw 7. Thus, by rotating the feed screw 7 it is possible to move the carriage 10 back and forth in the axial direction along the platen 6. Therefore, the print head 9 can print onto a paper 11 wound on the platen 6, one line by one line, under the condition of being fed ink from the ink tank 8 mounted on the carriage 10.
In general, this type of on-demand-type ink jet printer uses either a method of discharging ink from a nozzle by pressurizing the ink in accordance with the deformation of a piezoelectric element or a method of discharging ink in accordance with the pressure of bubbles produced by boiling the ink with an exothermic element. In the method of discharging ink from a nozzle by pressurizing the ink in accordance with the deformation of a piezoelectric element, a diaphragm is pressed by linearly displacing a piezoelectric element formed by superimposing several layers of piezoelectric material or a diaphragm is curved or deformed by applying a voltage to a piezoelectric element made of a single layer or two layers of piezoelectric material bonded to the diaphragm.
FIGS. 22 and 23(A) show the print head 9 of the printer 1 shown in FIG. 21 using a single-layer piezoelectric element as the printer head 9, which has an orifice plate 13 with a plurality of discharge nozzles 13A formed in it bonded to one side of a base 12 made of, for example, photosensitive glass and of a diaphragm 14 bonded to the other side of the base 12. A piezoelectric element 17 having electrodes 15 and 16 bonded to respective sides in the thickness direction is firmly bonded to the diaphragm 14 at positions corresponding to pressure chambers 12A formed in the base 12 by an adhesive or the like, not shown in the drawings.
In this case, as shown in FIG. 23(B), the pressure chamber 12A for storing ink and an ink introducing hole 12B communicating with the pressure chamber 12A are formed in the base 12. The pressure chamber 12A of the base 12 communicates with the corresponding discharge nozzle 13A of the orifice plate 13. Thus, the ink supplied from an external ink tank, not shown in FIG. 23(B), is injected through the ink introducing hole 12B and then stored in the pressure chamber 12A.
The piezoelectric element 17 comprises a bimorph element made of baked ceramic and has the feature in which, by applying a predetermined voltage between the electrodes 15 and 16 bonded to the both sides in the thickness direction, the element 17 is deformed in the thickness direction in accordance with the applied voltage. This feature is hereinafter referred to as the bimorph effect.
In the case of the print head 9, when applying a voltage to the piezoelectric element 17 in the initial state as shown in FIGS. 23(A) and 23(B), the piezoelectric element 17 shrinks inwardly and curves in the direction of the arrow "a" due to the bimorph effect of the piezoelectric element 17 and the diaphragm 14 and thereby, the and thereby the diaphragm 14 also curves in the direction of the arrow "a". Therefore, the displacement of the piezoelectric element 17 is transmitted to the pressure chamber 12A through the diaphragm 14. As a result, a pressure corresponding to the displacement of the piezoelectric element 17 is applied to the pressure chamber 12A, the volume of the pressure chamber 12A decreases and the pressure in the pressure chamber 12A rises, and thus the ink filling the pressure chamber 12A is discharged from the discharge nozzle 13A.
FIGS. 24(A) and 24(B) represent a cartridge-type ink tank 8. The tank 8 has a structure in which cartridge bodies 20A to 20C having the same structure are integrally formed corresponding to three colored inks such as magenta, cyan, and yellow.
In the case of the cartridge body 20A as shown in FIG. 24(B), an ink absorber storing chamber 20AX in which an ink absorber 21 is compressed and stored communicates with a closed-type ink storing chamber 20AY in which ink is stored through a communicating hole 20AZ formed at the bottom end of the chamber. A plurality of air introducing holes 20AH for introducing air to the inside are formed at the top side of the ink absorber storing chamber 20AX, and an ink feed port 20AS for feeding ink to the print head 9 is formed at the bottom side of the chamber 20AX. Cartridge bodies 20B and 20C are formed just like cartridge body 20A.
The ink absorber 21 itself is formed of, for example, a cellular material such as polyurethane foam made of a foaming material. By becoming impregnated and holding the ink, it is possible for the ink absorber 21 to prevent the ink from leaking from the ink feed port 20AS or from the air introducing holes 20AH.
When supplying the ink in the ink tank 8 to the print head 9, an injection needle, not shown in FIGS. 24(A) and 24(B), connected to the print head 9 is inserted into the ink absorber 21 through the feed port 20AS.
To feed ink to the print head 9 by using the ink tank 8, it is first necessary to make the ink absorber 21 hold an amount of ink slightly smaller than the maximum amount of ink that it can hold. Then, because a negative pressure is produced in the print head 9 due to the pressure produced by the displacement of the piezoelectric element 17 in the print head 9, as shown in FIG. 23(A), the ink held in the ink absorber 21 is conducted to the print head 9 through the injection needle.
In this case, because meniscuses are produced in the ink absorber 21 at the side of air introducing holes 20AH and generate a capillary force, that is, an ink soaking-up force, in the ink absorber 21, a predetermined negative pressure is produced in the ink absorber storing chamber 20AX. Therefore, it is possible to prevent an excessive amount of ink from leaking to the print head 9 from the ink absorber 21 and, thus, the print head 9 can perform stable discharge of ink droplets.
FIG. 25, in which the same reference numerals are applied to parts corresponding to those of FIG. 21, shows a tube-type serial ink jet printer 30. In the case of the ink jet printer 30, an ink tank 31 is arranged separately from a carriage 32 and communicates with a print head 34 fixed to the carriage 32 through an ink tube 33 connected to the ink tank 31. A tube pump 35 is set between the print head 34 and the ink tank 31, so as to feed the ink stored in the ink tank 31 to the print head 34 through the ink tube 33 by driving and controlling the tube pump 35.
FIG. 26 shows the internal structures of the ink tank 31 and the tube pump 35. In the case of the ink tank 31, an ink storing bag 37, whose front end is closed by a rubber cap 36, is set in a case body 31A, and a communicating ink needle 38 is inserted by passing it through the rubber cap 36. The communicating ink needle 38 places the ink storing bag 37 and the tube 33 in fluid communication, so that the ink in the ink storing bag 37 enters the tube 33 by passing through the communicating tube needle 38.
In the tube pump 35, a cylindrical space 35AX is formed in a body 35A, and a through-hole 35AY communicating with the space 35AX and the outside is formed in the body 35A. The tube 33 is inserted into the through-hole 35AY. In the space 35X, a rotating member 40 is attached to an output shaft 41 of a motor, not shown in FIG. 26, so as to rotate in the direction of the arrow "a" by using the output shaft 41 as a rotation center. Furthermore, a plurality of rollers 42A, 42B, 42C are mounted on the periphery of the rotating member 40, so as to freely rotate about their respective mounting centers. Rotating member 40 then rotates in the direction of the arrow "a" and rollers 42A, 42B, 42C rotate in the direction opposite to the direction of the arrow "a" about respective shafts arranged parallel with the output shaft 41 as roller rotation centers.
Thus, by rotating the rotating member 40 in the direction of the arrow "a" in response to driving by the motor, the tube 33 in the space 35AX is successively pressed by the rollers 42A, 42B, 42C, whereby the ink in the tube 33 is ejected to the print head 34. The ink supply amount can be adjusted by controlling the motor rotation rate, so that as a result the print head 34 can perform stable discharge of ink droplets.
In the carriage-mounting-type ink jet printer 1, the ink tank 8 shown as FIGS. 24(A) and 24(B) is in the form of a cartridge having the ink absorber 21 built in. Therefore, there is the advantage that the entire structure of the printer 1 can be simplified and reduced in size. Nevertheless, the amount of ink that can be stored is relatively small compared to the entire volume of the ink tank 8 and the amount of ink that can be impregnated by the ink absorber 21 is restricted by the material and quantity of the ink absorber 21. Therefore, there is a problem that it is very difficult to store a large amount of ink in the ink tank 8. Moreover, because a negative pressure in the ink tank is adjusted by the ink absorber, there are also the problems that it is impossible to completely prevent ink from leaking to the print head or from being insufficiently fed to the print head.
On the other hand, in the tube-type ink jet printer 30, because the ink tank 31 shown in FIG. 25 is arranged separate and apart from the print head 34, there is the advantage that larger and larger amounts of ink can be stored in the ink tank simply by increasing the volume of the tank. Nevertheless, an ink feed source such as the tube pump 35 or a valve mechanism (not shown) is necessary to feed the ink stored in the ink tank 31 to the print head 34. Therefore, there is a problem that it is difficult to reduce the size of the entire printer and simplify the overall structure. Moreover, the tube 33 is typically connected for a long distance between the print head 34 and the ink tank 31, so that the ink feed is easily interrupted and air that is dissolved in the ink in the tube 33 may appear as bubbles when the tube 33 is physically deflected. In that case, there is the problem that not only ink but also air bubbles may enter the print head 34 through the tube 33 and the feed of ink to the print head is interrupted.